Cathode ray tube whose image screen is both cathodochromic and fluorescent and the material for the screen

ABSTRACT

A cathode ray tube (CRT) having an image screen composed of a material that is both cathodochromic and fluorescent and in which the cathodochromic coloration lifetime is at least a month. The material employed is Na6 Al6 (GeySi1 y)6 O24.2(1-z) NaX wherein z is the fraction of NaX vacancies, X is chosen from the group consisting essentially of chlorine, bromine, OH and iodine and mixtures thereof, and y varies from 0.003 to 0.30.

0 United States Patent 1191 [111 3,91 1,315

Todd, Jr. et a1. Oct. 7, 1975 [54] CATHODE RAY TUBE WHOSE IMAGE3,253,497 5/1966 Dreyer 315/85 X SCREEN IS BOTH CATHODOCHROMIC 3,339,0998/1967 Anderson... 313/398 3,452,332 6/1969 Bron et al.. 315/85 X ANDFLUORESCENT AND THE MATERIAL 3,631,295 12/1971 Pooley 315/13 ST FOR THESCREEN 3,650,975 3/1972 Yale 252/3014 x [75] Inventors: Lee T. Todd,Jr., Lexington, Ky.;

23 ne :1 g 2" t i g f Primary Examiner-James W. Lawrence M nc es 0 0Assistant Examiner-E. R. La Roche Attorney, Agent, or FirmArthur A.Smith, Jr.; [73] Assignee: Massachusetts Institute of Robert Shaw;Martin M. Santa.

Technology, Cambridge, Mass.

[22] Filed: Apr. 1, 1974 [57] ABSTRACT [2]] App]. No.: 456,961

A cathode ray tube (CRT) having an image screen [52] us Cl 313/391.252/301 4 313/397. composed of a material that is both cathodochromic313/398. 515/13 and fluorescent and in which the cathodochromic col 511111. C1 1101.] 29/20- 11011 31/12 oration lifetime is at least a Thematerial [58] Field of Search 313 391, 397, 398, 101, PlOYed is NafiA16(GeuSi1-1/)6 024201) Nax wherein 313/311. 315/85 10 13 346/74 z isthe fraction of NaX vacancies, X is chosen from 5 5 3675523014 the groupconsisting essentially of chlorine, bromine, OH and iodine and mixturesthereof, and varies from [56] References Cited 0003 to UNITED STATESPATENTS 23 Claims, 4 Drawing Figures 2,752,521 6/1956 lvey .1 313/465 x1 X x t K I i x 2 M j i 2 I r I F 4fip US. Patent 0m. 7,1975 Sheet 1 of2 3,911,315

XXX

US. Patent Oct. 7,1975 Sheet 2 of 2 3,911,315

Wavelength (A) FIG. 3A

3 5 P6598 2909:... wucmumw E Wavelength (A) FIG. 3B

CATHODE RAY TUBE WHOSE IMAGE SCREEN IS 80TH CATHODOCHROMIC ANDFLUORESCENT AND THE MATERIAL FOR THE SCREEN The invention describedherein was made in the course of or under a grant from the NationalScience Foundation, an agency of the United States Government.

The present invention relates to a cathode ray tube whose image screenis both cathodochromic and fluorescent, to the material of which theimage screen is composed, and to the means of excitation of saidfluorescence.

Attention is called to the following related applications being filedherewith and hereby incorporated herein by reference: Method of andApparatus for Exciting Luminescence in a Cathode Ray Tube Having AnImage Screen Composed of a Material that Is Both Cathodoehromic andCathodoluminescent, Ser. No. 457,112, filed Apr. 1, 1974 (Todd, Jr.); AProcess for Preparing cathodochromic Sodalite Having Enhanced ColorationProperties and a Cathode Ray Tube Employing the Same, Ser. No. 456,962,filed Apr. 1, 1974 (Todd, Jr. et al.), Cathode Ray Tube EmployingFaceplateDeposited cathodochromic Material and Electron Beam Erase, Ser.No. 457,1 1 1, filed Apr. 1, 1974 (Todd, Jr.). Attention is called alsoto the doctoral thesis of Lee T. Todd, Jr. (a copy of the thesisaccompanies the application entitled A Process for PreparingCathodochromic Mixtures Having Enhanced Coloration Properties"), whichthesis is hereby incorporated herein by reference; the work upon whichthe thesis is based was done by the inventor Todd, Jr. at M.1.T. underthe supervision of the inventor Linz and with the collaboration andconsultation, as to certain aspects thereof, with the inventor Farrell.The thesis contains an exhaustive list of references to prior work aswell as detailed theoretical analysis, neither of which is repeatedhere. The following US. Pat. Nos. are made of record: 3,705,323(Shidlovsky); 3,598,750 (Phillips); 2,752,521 (Ivey); 2,761,8463,706,845 (Heyman et a1.); 3,148,281 (Fyler).

Photochromic materials have the property that they change colorreversibly upon illumination by light while cathodochromic materialschange color upon excitation by an electron beam. This is not a cleardistinction, however, since most photochromic materials are alsocathodochromic. A unique distinction can be made if one considers thebleaching or erasing mode. In photochromic materials the colored statecan be completely bleached by light while in the cathodochromicmaterials light causes only partial bleaching. The remaining coloration,thermal mode coloration, must be erased by heating. The lifetime of thiscoloration at room temperature is, in some cases, greater than severalmonths even under bright ambient light. The coloration can be erasedrapidly by heating the material to about 200C for sodalite. The systemsdescribed herein relate to sodalite operating in the thermal erase mode.

Cathode ray tube (CRT) image screens for cathodochromic materialsexhibit high resolution, long lifetime of coloration, gray scale andhigh contrast in bright ambient light. However, since their contrastcapability depends on reflected or transmitted light, they cannot beviewed satisfactorily under low ambient conditions. The fluorescencewhich is herein disclosed allows the use of such image screens in bothhigh and low ambient light levels. In bright ambient the screen has its(Medved); 4

normal cathodochromic properties. In low ambient, under ultravioletlight, the unwritten area of the screen becomes bright green while thewritten area remains dark. There is actually a contrast ratioenhancement of about a factor of two. A cathodochromic screen imageviewed in bright ambient light with a contrast ratio of about 10:1exhibits a contrast ratio of 22:1 when viewed in low ambient underultraviolet light.

A cathodochromic display device operated in the fluorescent mode is morevisually acceptable than present phosphor displays since the viewer seesa dark display on a light background. The brightness of the backgroundcan be easily adjusted by varying the intensity of the ultravioletillumination. In this circumstance the viewer must be shielded from theultraviolet light by a special absorbing faceplate. If the faceplate ischosen such that it passes only the green fluorescent light, contrastratios in excess of 40:1 can easily be achieved in the fluorescent mode.

There are numerous systems in which the fluorescent-mode display can beemployed. In airplane cockpits where low light levels are oftennecessary, this display offers high resolution, long storage time andhigh contrast. Even in brightly illuminated areas, the display remainsintact and still has high contrast. The same system exists for displaysin patrol ears, helicopters and ships. For any night vision use in whichphosphor display devices have been employed these fluorescentmodecathodochromic CRTs offer the advantages of high resolution and longstorage time and, possibly, even lower cost.

As is noted in said thesis, luminescent properties of doped sodalitehave been studied and reported by numerous investigators. Sulphur is themost common dopant, but oxygen, manganese and iron have also beenemployed. All the previously proposed dopants degrade the cathodochromiccharacteristics of the sodalite while enhancing the photochromiccharacteristics. On CRT image screens such materials erase quickly; animage lasts about five minutes in high ambient light and about 15minutes in the dark. In contrast, some of the present materials havebeen maintained for months in an offiee having fluorescent ceilinglights and one wall of windows without notable change in coloration.

Accordingly, it is a principal object of the invention to provide acathode ray tube having an image screen composed of cathodochromicsodalite that displays high contrast in high ambient light and is, aswell, fluorescent under ultraviolet radiation, thus offering contrast inlow ambient light conditions.

A further object is to provide a high resolution cathode ray tubecomprising cathodochromic sodalite material.

Another object is to provide a material for such image screen, amaterial that gives high contrast under the conditions noted and onethat has a long lifetime of coloration of the order of months or years.

Still another object is to provide an image screen material that has acontrast ratio or the order of 10:1 in high ambient light andapproximately double that ratio in ultraviolet radiations.

These and still further objects are apparent in the description thatfollows and are particularly delineated in the appended claims.

The fogegoing objects are attained in a cathode ray tube having an imagescreen composed of a material that is both cathodochromic andfluorescent and in which the screen material has a coloration lifetimeof weeks, months or years. The cathode ray tube comprises any envelopehaving a faceplate upon which the image screen is formed and means forproviding an electron beam to write upon the image screen. The screenmaterial is sodalite with a dopant that alters the electronic structureof the material and thus allows fluorescence to occur under ultravioletexcitation, for example. The cathodochromic and fluorescent image screenmaterial discussed herein is Na Al (Ge,,Si .2( l-z)NaX, wherein z in thefraction of NaX vacancies, X is chosen from the group consisting ofchlorine, bromine, OH and iodine and mixtures thereof, and y varies fromabout 0.003 to 0.30.

The invention is hereinafter discussed with reference to theaccompanying drawing in which:

FIG. 1 is a side view, partially cutaway, of a cathode ray tube (CRT)embodying the present inventive concepts and shows a tube having atransparent conductive coating on the faceplate of the CRT and betweensaid faceplate and the image screen thereof;

FIG. 2 is a partial view, in section, showing a modification of thecathode ray tube of FIG. 1, the image screen in the latter figure beingdisposed between the conductive coating and the faceplate;

FIG. 3A is fluorescence spectrum of Ge doped bromine sodalite at 77K;and

FIG. 3B is the excitation spectrum of the Ge doped bromine sodalite at77K.

Referring now to FIG. 1, a cathode ray tube embodying the presentconcepts is shown at 101 comprising an envelope 1 having a faceplate 2.There is within said envelope a cathodochromic image screen 3 disposedupon a transparent conductive coating 4 of SnO for example, that servesas the anode of the electron beam producing means later discussed. Itshould be noted here that the use of a transparent anode is only onevariation of the two exemplary possibilities herein discussed. Also, theimage screen here is shown as part of a composite structure adhered tothe inside surface of the faceplate 2 and this particular typearrangement has advantages, particularly in terms of cost of manufactureand structural stability, but the present concepts have use in cathoderay tubes wherein the image screen is physically displaced from thefaceplate of the tube and deposited on another substrate.

The image screen is made of the cathodochromic and fluorescent materialNa Al (Ge,,Si 0 .2( l-z)NaX, wherein X is chosen from the groupconsisting essentially of chlorine, bromine, OH and iodine and mixturesthereof, y varies from about 0.003 to 0.30 and z is the fraction of NaXvacancies created during hydrogen annealing. A value of y of the orderof 0.01 (i.e., l percent) has been found to give optimum fluorescentcharacteristics. Annealing of the material in hydrogen is necessary tocreate negative ion vacanies which are essential for color centerformation, in this case, F centers. This process is also required forthe occurrence of fluorescence. The fluorescent and excitation spectrumof an annealed germanium doped bromine sodalite power are shown in FIGS.3A and 3B, respectively. The emission band peaks at 5250A when excitedby 2750A or 3400A radiation. Upon electron beam exposure, the materialcolors and acquires an F absorption band at approximately 5500A. Sincethe absorption band occurs very close to the emission band, much of thefluorescence created within the colored portions of the image screen isre-absorbed. Additional atomic quenching also occurs leading to a veryhigh contrast between the colored and uncolored areas. The colorationlifetime of this material is of the order of months and even years.

Writing on the image screen is effected by an electron beam provided byan electron gun 5 and the anode in combination. The anode configurationdepends on the means of ultraviolet excitation of the fluorescence andis discussed in detail below. It is not believed that any furtherdiscussion of electron beam producting, focusing and deflection need bepursued since these are matters well within the scope of workers in theart. Erasing the image, as above noted, is effected by raising thetemperature of the cathodochromic sodalite screen material. This can beaccomplished by resistive heating with the image screen deposited on athin substrate within the envelope, (see US. Pat. No. 3,700,804) or byelectron beam heating with the material again deposited on a substratewithin the tube (see thesis references), but a preferred system oferasure is the use of the electron beam that is used for writing, asdisclosed in the application entitled Cathode Ray Tube EmployingFaceplate-Deposited Cathodochromic Material and Electron Beam Erase.

The fluorescent and cathodochromic CRT can be operated in either of twomodes rear or front illumination. One form of CRT fabrication used forrear illumination is that shown in FIG. 1. In this case, the image iswritten on the screen 3 by the electron beam produced by an electron gun5 in combination with an anode, as noted. The anode comprises atransparent conductive coating 4 on the inside surface of the faceplate2 between the faceplate and the image screen 3 and extending at 6 alongthe side walls labeled 7 of the envelope toward the electron gun 5; analuminum or Aquadag coating 8 which overlaps the transparent conductivelayer 4 extends further along the sidewalls 7; and an Aquadag coating 9which overlaps the coating 8 and extends along the tube neck 10 to theelectron gun 5. In high ambient light, the image is read in atransmission mode using a lamp 1] which directs visible radiation (whitelight) through the screen 3 toward the viewer. The uncolored portions ofthe screen transmit the viewing light while the colored areas absorb itthus creating a high contrast image. In low ambient conditions, wherewhite light is not allowed, the image is read in the fluorescent modewith the fluorescence being excited by one or more ultraviolet lamps 12which direct radiation upon the surface designated 13 of the screenfacing the electron gun. Alternatively, the excitation source 14 may belocated outside of the envelope, as shown in FIG. 1 with the excitingradiation entering through a rear port 15 and striking the screensurface designated 13. In this case, the port cover 16 must be amaterial, such as quartz, which transmits the exciting light. In both ofthe above low ambient situations, the faceplate 2, or an auxilliaryfilter, must absorb the ultraviolet radiation to protect the viewer.

In the front illumination configuration, the screen construction is asshown in FIG. 2. The image screen 3 is deposited directly on thefaceplate 2 and the anode consists of an opaque conductive coating 17,usually aluminum, on the back surface 18 of the screen and extendingalong the sidewalls 7 of the envelope to the tube neck where the anodecircuit is completed with an Aquadag coating 9, as before. In operation,the image is written by the electron beam and read, in high ambientconditions, with light incident on the front surface 19 of the imagescreen. The uncolored areas of the screen reflect the incident lightwhile the colored areas partially absorb the reading light and reflectthe remainder thus causing a colored image. ln low ambient conditions,the screen fluorescence is excited by one or more ultraviolet lights 20outside the envelope which direct radiation upon the front surface 19 ofthe image screen. Of course, in this situation, the faceplate 2 musttransmit the ultraviolet radiation. The aluminum layer 17 serves severalpurposes in this configuration: 1) it is part of the anode; (2) in highambient conditions, it reflects the incident viewing light back throughthe image screen thus increasing its whiteness and hence its contrastcapability; (3) in the fluorescent mode, it reflects the incidentultraviolet radiation back through the screen and thus increases theultraviolet exposure; and (4) in this latter mode, it also reflects thegreen fluorescent light which is directed away from the viewer backtoward the viewer thus increasing the fluorescent light output.

Further means for effecting fluorescence of the image screen 4 isdisclosed in the application entitled Method of and Apparatus forExciting Luminescence in a Cathode Ray Tube Having an Image ScreenComposed of a Material that Is Both Cathodochromic and Fluorescent.

There follows now three examples relating to the growth of thefluorescent sodalite material of the present invention, with its smallpercentage of germanium dopant.

EXAMPLE 1 Chemicals are combined according to the equation:

ZNaBR 3.41 0,, 5.82 0.18 060 6NaOH- Na Al si .,,oe o .ZNaBr 31-1 0 toyield bromine sodalite containing three atomic percent germaniumsubstituted for silicon. 4. 12 grams NaBr, 6.12 grams A1 0 6.99 gramsSiO 0.37 grams GeO are throughly mixed and placed in a silver-linedhydrothermal pressure vessel with an internal capacity of approximately130 ml. Ninety milliliters of a solution of H 0 and 40.0 grams NaOH arethen added to the charge within the vessel and the vessel sealed. Thelower portion of the vessel is maintained at about 368C and the upperportion at 330C for about 31 hours and the vessel is then allowed tocool to room temperature. The product is a slurry of crystalline powderin a concentrated NaOH solution. The NaOH is removed by washing thepowder repeatedly with distilled water. Next, the powder is dried forone hour in an oven at about 130C and then crushed to a fine particlesize. At this point, the X-ray powder pattern consists of diffractionpeaks representing single phase germanium doped sodalite. (Electronmicroprobe measurements made in work done revealed that the powdercontained only one atomic percent germanium substituted for siliconrather than the intended three atomic percent due to the incompletesubstitution of the larger germanium ions for the smaller silicon ions.)

The powder is annealed in hydrogen to create lattice vacancies which arenecessary for the formation of color centers, in this case F centers.The hydrogen annealing treatment is also essential for the occurrence offluorescence. When annealed in hydrogen at about 650C for fifteenminutes, the above powder has an absorption band at 5400A and anemission band at 5250A.

EXAMPLE 2 Chemicals are combined according to the equation:

to yield bromine sodalite containing seventy-five atomic percentgermanium substituted for silicon. 4.12 grams NaBr, 6.12 grams A1 01.802 grams SiO 9.414 GeO are throughly mixed and placed in asilverlined hydrothermal pressure vessel with an internal capacity ofapproximately 130 ml. 92 milliliters of a solution of H 0 and 40 gramsNaOH are then added to the charge within the vessel and the vesselsealed. The lower portion of the vessel is maintained at about 370C andthe upper portion at 330C for about 25 hours and the vessel is thenallowed to cool to room temperature. The product is processed as inExample 1 to yield a fine particle sodalite powder. (Electron microprobemeasurements made in work done revealed that the powder contained only28 atomic percent ger manium substituted for silicon rather than theintended atomic percent.) When annealed in hydrogen to 600C for 15minutes, the powder exhibits an absorp tion band at 5515A and anemission band at 5250A.

EXAMPLE 3 Germanium doped sodalite bromine is also produced by acombination of sintering and hydrothermal methods. Chemicals arecombined according to the equa tion:

to yield bromine sodalite containing 10 atomic percent germaniumsubstituted for silicon. 4.12 grams NaBr, 6.12 grams A1 0 6.49 grams SiO1.26 grams GeO and 4.80 grams NaOH are thoroughly mixed and thensintered in a furnace at 750C for 2 hours. The resulting product, in theform of a hard calcined mass, is next ball milled for several hours toreduce it to a fine-grain powder.

The sintered powder is next reacted in a hydrothermal vessel at lowtemperature. 3.14 grams of sintered powder are placed in a teflon'linedacid digestion vessel with an internal capacity of 30 ml. An 18 mlsolution of 7.20 grams NaOH and H 0 are added to the charge in thevessel and the vessel sealed. The base of the vessel is maintained at130C for about hours and then cooled to room temperature. The resultantis a slurry of crystalline powder in a concentrated NaOl-l solution. Theproduct is then processed as in Example 1. After annealing for 15minutes at about 650C, the material exhibits an absorption band at 5500Aand an emission band at 5250A.

Modifications of the invention herein disclosed will occur to personsskilled in the art and all such modifications are deemed to be withinthe spirit and scope of the invention as defined by the appended claims:

What is claimed is:

1. A cathode ray tube that comprises an envelope having a faceplate, acathodochromic image screen in said envelope, said cathodochromic imagescreen comprising a material that has a coloration or F-center as wellas a luminescent or fluorescent center so that said material iscathodochromic and is also fluorescent, the coloration or F-centerabsorption band of said material occurring very close to the emissionband of the luminescent of fluorescent center; and means for producingan electron beam to write on the image screen.

2. A cathode ray tube as claimed in claim 1 in which the electron beamproducing means includes an electron gun and an anode, in which theanode is a transparent conductive coating on the faceplate, and whichincludes aluminum on the inside surface of the envelope side walls andconnected to the transparent conductive coating such that the anodecircuit is complete.

3. A cathode ray tube as claimed in claim 1 in which said material is NaAl (Ge Si, O 2( l-z)NaX, wherein X is chosen from the group consistingessentially of chlorine, bromine, OH and iodine and mixtures thereof, yvaries from about 0.003 to 0.30, z is the fraction of NaX vacancies, andZ 1.

4. A tube as claimed in claim 3 in which the NaX vacancies are createdby hydrogen annealing.

5. A tube as claimed in claim 3 in which the NaX vacancies are createdby hydrogen annealing in a temperature range of about 500C to 900C for atime period of at least 5 minutes.

6. A cathode ray tube as claimed in claim 3 in which y is the order of0.01 and X is bromine.

7. A cathode ray tube as claimed in claim 1 that further includesultraviolet light means positioned to direct radiation upon said screen.

8. A cathode ray tube as claimed in claim 7 in which the means toproduce the electron beam is an electron gun and an anode, in which theanode is a thin aluminum layer on the major surface of the screen andbetween the screen and the electron gun, and in which the ultravioletradiation is directed upon the other major surface of the screen.

9. A cathode ray tube as claimed in claim 7 in which the means toproduce the electron beam includes an electron gun and an anode, and inwhich the anode is a transparent conductive coating on the insidesurface of the faceplate between the envelope and the screen andextending along the side walls of the envelope toward the electron gun.

10. A cathode ray tube as claimed in claim 7 in which the means toproduce the electron beam is an electron gun and an anode, in which theanode is a transparent conductive coating on the inside surface of thefaceplate between the envelope and the screen and extends along the sidewalls of the envelope toward the electron gun and in which theultraviolet light means directs ultraviolet radiation upon the surfaceof the screen facing the electron gun.

11. A cathode ray tube as claimed in claim 10 in which the ultravioletlight means is outside the envelope and in which the envelope transmitsultraviolet radiation to the screen.

12. A cathode ray tube as claimed in claim 10 in which the ultravioletlight means is inside the envelope.

13. A fluorescent and cathodochromic material that comprises Na Al -(GeSi O 2(l-z)NaX, wherein z is the fraction of NaX vacancies, X is chosenfrom the group consisting essentially of chlorine, bromine, OH andiodine and mixtures thereof and y varies from about 0.003 to 0.30.

14. A material as claimed in claim 13 wherein X is a mixture of OH andbromine and y is the order of 0.01.

15. A material as claimed in claim 13 in which y is the order of 0.01and wherein X is bromine.

16. A fluorescent and cathodochromic material as claimed in claim 13 andin which the fluorescent emission band is centered at about 5250A andthe cathodochromic absorption band is about 5500A.

17. A fluorescent and cathodochromic material as claimed in claim 16 inwhich the cathodochromic coloration lifetime is at least a month.

18. A fluorescent and cathodochromic material that consists essentiallyof l la Al (Ge,,Si O, 2(1- z)NaX, wherein X is bromine y varies from0.003 to 0.30 and z is greater than zero but less than 1.

19. A material as claimed in claim 18 in which X includes both bromineand OH.

20. A cathode ray tube that comprises an envelope having a faceplate,image screen means that has a coloration or F-center as well as aluminescent of fluorescent center so that the image screen means is bothcathodochromic and fluorescent, the coloration or F- center absorptionband of the image screen means occurring very close to the emission bandof the luminescent or fluorescent center, the cathodochromic colorationlifetime being at least the order of hours, means producing an electronbeam to write on the image screen, and means effecting luminescence ofthe image screen.

21. Apparatus as claimed in claim 20 in which the image screen comprisesa cathodochromic and fluorescent sodalite material that contains adopant that alters the electronic structure of the material such thatfluorescence occurs.

22. Apparatus as claimed in claim 21 in which said dopant is germaniumin the atomic percent range from 0.3 percent to 30 percent.

23. Apparatus as claimed in claim 20 that further includes meansilluminating the image screen in the visible range of theelectromagnetic spectrum.

1. A cathode ray tube that comprises an envelope having a faceplate, acathodochromic image screen in said envelope, said cathodochromic imagescreen comprising a material that has a coloration or F-center as wellas a luminescent or fluorescent center so that said material iscathodochromic and is also fluorescent, the coloration or F-centerabsorption band of said material occurring very close to the emissionband of the luminescent of fluorescent center; and means for producingan electron beam to write on the image screen.
 2. A cathode ray tube asclaimed in claim 1 in which the electron beam producing means includesan electron gun and an anode, in which the anode is a transparentconductive coating on the faceplate, and which includes aluminum on theinside surface of the envelope side walls and connected to thetransparent conductive coating such that the anode circuit is complete.3. A cathode ray tube as claimed in claim 1 in which said material isNa6Al6(GeySi1-y)6 O24 . 2(1-z)NaX, wherein X is chosen from the groupconsisting essentially of chlorine, bromine, OH and iodine and mixturesthereof, y varies from about 0.003 to 0.30, z is the fraction of NaXvacancies, and 0<Z<1.
 4. A tube as claimed in claim 3 in which the NaXvacancies are created by hydrogen annealing.
 5. A tube as claimed inclaim 3 in which the NaX vacancies are created by hydrogen annealing ina temperature range of about 500*C to 900*C for a time period of atleast 5 minutes.
 6. A cathode ray tube as claimed in claim 3 in which yis the order of 0.01 and X is bromine.
 7. A cathode ray tube as claimedin claim 1 that further includes ultraviolet light means positioned todirect radiation upon said screen.
 8. A cathode ray tube as claimed inclaim 7 in which the means to produce the electron beam is an electrongun and an anode, in which the anode is a thin aluminum layer on themajor surface of the screen and between the screen and the electron gun,and in which the ultraviolet radiation is directed upon the other majorsurface of the screen.
 9. A cathode ray tube as claimed in claim 7 inwhich the means to produce the electron beam includes an electron gunand an anode, and in which the anode is a transparent conductive coatingon the inside surface of the faceplate between the envelope and thescreen and extending along the side walls of the envelope toward theelectron gun.
 10. A cathode ray tube as claimed in claim 7 in which themeans to produce the electron beam is an electron gun and an anode, inwhich the anode is a transparent conductive coating on the insidesurface of the faceplate between the envelope and the screen and extendsalong the side walls of the envelope toward the electron gun and inwhich the ultraviolet light means directs ultraviolet radiation upon thesurface of the screen facing the electron gun.
 11. A cathode ray tube asclaimed in claim 10 in which the ultraviolet light means is outside theenvelope and in which the envelope transmits ultraviolet radiation tothe screen.
 12. A cathode ray tube as claimed in claim 10 in which theultraviolet light means is inside the envelope.
 13. A fluorescent andcathodochromic material that comprises Na6Al6(GeySi1-y)6 O24 .2(1-z)NaX, wherein z is the fraction of NaX vacancies, X is chosen fromthe group consisting essentially of chlorine, bromine, OH and iodine andmixtures thereof and y varies from about 0.003 to 0.30.
 14. A materialas claimed in claim 13 wherein X is a mixture of OH and bromine and y isthe order of 0.01.
 15. A material as claimed in claim 13 in which y isthe order of 0.01 and wherein X is bromine.
 16. A fluorescent andcathodochromic material as claimed in claim 13 and in which thefluorescent emission band is centered at about 5250A and thecathodochromic absorption band is about 5500A.
 17. A fluorescent andcathodochromic material as claimed in claim 16 in which thecathodochromic coloration lifetime is at least a month.
 18. Afluorescent and cathodochromic material that consists essentially ofNa6Al6(GeySi1-y)6 O24 . 2(1-z)NaX, wherein X is bromine y varies from0.003 to 0.30 and z is greater than zero but less than
 1. 19. A materialas claimed in claim 18 in which X includes both bromine and OH.
 20. Acathode ray tube that comprises an envelope having a faceplate, imagescreen means that has a coloration or F-center as well as a luminescentof fluorescent center so that the image screen means is bothcathodochromic and fluorescent, the coloration or F-center absorptionband of the image screen means occurring very close to the emission bandof the luminescent or fluoreScent center, the cathodochromic colorationlifetime being at least the order of hours, means producing an electronbeam to write on the image screen, and means effecting luminescence ofthe image screen.
 21. Apparatus as claimed in claim 20 in which theimage screen comprises a cathodochromic and fluorescent sodalitematerial that contains a dopant that alters the electronic structure ofthe material such that fluorescence occurs.
 22. Apparatus as claimed inclaim 21 in which said dopant is germanium in the atomic percent rangefrom 0.3 percent to 30 percent.
 23. Apparatus as claimed in claim 20that further includes means illuminating the image screen in the visiblerange of the electromagnetic spectrum.